The present invention relates to generally a self-scanning light-emitting device, particularly to a self-scanning light-emitting device whose amount of light may be corrected.
A light-emitting device in which a plurality of light-emitting elements are arrayed on the same substrate is utilized as a light source of a printer, in combination with a driver circuit. The inventors of the present invention have interested in a three-terminal light-emitting thyristor having a pnpn-structure as an element of the light-emitting device, and have already filed several patent applications (see Japanese Patent Publication Nos. 1-238962, 2-14584, 292650, and 2-92651.) These publications have disclosed that a self-scanning function for light-emitting elements may be implemented, and further have disclosed that such selfscanning light-emitting device has a simple and compact structure for a light source of a printer, and has smaller arranging pitch of thyristors.
The inventors have further provided a self-scanning light-emitting device having such structure that an array of light-emitting thyristors having transfer function is separated from an array of light-emitting thyristors having writable function (see Japanese Patent Publication No. 2-263668.)
Referring to FIG. 1, there is shown an equivalent circuit diagram of a fundamental structure of this self-scanning light-emitting device. According to this structure, the device comprises transfer elements T1, T2, T3 . . . and writable light-emitting elements L1, L2, L3 . . . , these elements consisting of three-terminal light-emitting thyristors. The structure of the portion of an array of transfer elements includes diode D1, D2, D3 . . . as means for electrically connecting the gate electrodes of the neighboring transfer elements to each other. VGK is a power supply (normally 5 volts), and is connected to all of the gate electrodes G1, G2, G3 . . . of the transfer elements via a load resistor RL, respectively. Respective gate electrodes G1, G2, G3 . . . are correspondingly connected to the gate electrodes of the writable light-emitting elements L1, L2, L3 . . . . A start pulse xcfx86s is applied to the gate electrode of the transfer element T1, transfer clock pulses xcfx861 and xcfx862 are alternately applied to all of the anode electrodes of the transfer elements, and a write signal xcfx86I is applied to all of the anode electrodes of the light-emitting elements. The self-scanning light-emitting device shown in FIG. 1 is a cathode common type, because all of the cathodes of the transfer elements and the light-emitting elements are commonly connected to the ground.
Referring to FIG. 2, there are shown respective wave shapes of the start pulse xcfx86s, the transfer clock pulses xcfx861, xcfx862, and the write pulse signal xcfx86I. The ratio (i.e., duty ratio) between the time duration of high level and that of low level in each of clock pulses xcfx861 and xcfx862 is substantially 1 to 1.
The operation of this self-scanning light-emitting device will now be described briefly. Assume that as the transfer clock xcfx861 is driven to a high level, the transfer element T2 is now turned on. At this time, the voltage of the gate electrode G2 is dropped to a level near zero volts from 5 volts. The effect of this voltage drop is transferred to the gate electrode G3 via the diode D2 to cause the voltage of the gate electrode G3 to set about 1 volt which is a forward rise voltage (equal to the diffusion potential) of the diode D2. On the other hand, the diode D1 is reverse-biased so that the potential is not conducted to the gate G1, then the potential of the gate electrode G1 remaining at 5 volts. The turn on voltage of the light-emitting thyristor is approximated to a gate electrode potential+a diffusion potential of PN junction (about 1 volt.) Therefore, if a high level of a next transfer clock pulse xcfx862 is set to the voltage larger than about 2 volts (which is required to turnon the transfer element T3) and smaller than about 4 volts (which is required to turn on the transfer element T5), then only the transfer element T3 is turned on and other transfer elements remain off-state, respectively. As a result of which, on-state is transferred from T2 to T3. In this manner, on-state of transfer elements are sequentially transferred by means of two-phase clock pulses.
The start pulse xcfx86s works for starting the transfer operation described above. When the start pulse xcfx86s is driven to a low level (about 0 volt) and the transfer clock pulse xcfx862 is driven to a high level (about 2-4 volts) at the same time, the transfer element T1 is turned on. Just after that, the start pulse xcfx86s is returned to a high level.
Assuming that the transfer element T2 is in the on-state, the voltage of the gate electrode G2 is lowered to almost zero volt. Consequently, if the voltage of the write signal xcfx86I is higher than the diffusion potential (about 1 volt) of the PN junction, the light-emitting element L2 may be turned into an on-state (a light-emitting state).
On the other hand, the voltage of the gate electrode G1, is about 5 volts, and the voltage of the gate electrode G3 is about 1 volt. Consequently, the write voltage of the light-emitting element L1 is about 6 volts, and the write voltage of the light-emitting element L3 is about 2 volts. It follows from this that the voltage of the write signal xcfx86I which can write into only the light-emitting element L2 is in a range of about 1-2 volts. When the light-emitting element L2 is turned on, that is, in the light-emitting state, the amount of light thereof is determined by the write signal xcfx86I. Accordingly, the light-emitting elements may emit light at any desired amount of light. In order to transfer on-state to the next element, it is necessary to first turn off the element in on-state by temporarily dropping the voltage of the write signal xcfx86I down to zero volts.
The self-scanning light-emitting device described above may be fabricated by arranging a plurality of luminescent chips each thereof is for example 600 dpi (dots per inch)/128 light-emitting elements and has a length of about 5.4 mm. These luminescent chips may be obtained by dicing a wafer in which a plurality of chips are fabricated. While the distribution of amounts of light of light-emitting elements in one chip is small, the distribution of amounts of light among chips is large. Referring to FIGS. 3A and 3B, there is shown an example of the distribution of amounts of light in a wafer. FIG. 3A shows a plan view a three-inch wafer 10, wherein an x-y coordinate system is designated. The light-emitting elements are arranged in a direction of x-axis, and the length of one luminescent chip is about 5.4 mm. FIG. 3B shows the distribution of amounts of light at locations in the x-y coordinate system. It should be noted in FIG. 3B that the amount of light is normalized by an average value within a wafer. In FIG. 3B, four distributions of amounts of light are shown, with y-locations being different (i.e., y=0, 0.5, 1.0, and 1.35 inches).
It is apparent from FIG. 3B that each distribution of amounts of light in a chip is within the deviation of at most xc2x10.5% except chips around the extreme peripheral part of a wafer, but the average values of amounts of light in respective chips on a wafer are distributed in a range of the deviation of about 6%, because the amounts of light in a wafer are distributed like the shape of the bottom of a pan as shown in FIG. 3B. It has been noted that another wafers have distributions similar to that of FIG. 3B, and average values of amounts of light are varied among wafers. In this manner, while the amounts of light are distributed in a small range in a chip, the average values of amount of light of respective chips in a wafer are distributed broadly.
Therefore, a self-scanning light-emitting device having a uniform distribution of amounts of light has provided heretofore by arranging luminescent chips whose average values of amounts of light are substantially the same. For example, in order to hold the distribution of average values of amounts of light of chips constituting one self-scanning light-emitting device into the deviation of xc2x11%, luminescent chips are required to be grouped into a plurality of ranks each having xc2x11% deviation of average values of amounts of light to arrange chips included in the same rank in fabricating a self-scanning light-emitting device (see Japanese Patent Publication No. 9-319178).
In fact, the resistance of resistors in the self-scanning light-emitting device and the output impedance of a driver circuit for the self-scanning light-emitting device have errors, respectively, so that the deviation of average value of amounts of light for one rank is required to further be decreased. In order to decrease the dispersion of the output impedance of a driver circuit, the output impedance itself is needed to be decreased, resulting in increasing of the area of a chip and the cost thereof. Furthermore, when the self-scanning light-emitting device is used for an optical device such as a printer, the accuracy of a lens system is required.
If the number of ranks for average values of amounts of light is large, the work for grouping chips into ranks is not only very complicated but also has a poor manufacturing efficiency because many kinds of stoked chips are required.
The object of the present invention is to provide a self-scanning light-emitting device in which the distribution of amounts of light may be corrected in a chip or among chips by regulating the amount of light for a light-emitting element.
According to a first aspect of the present invention, a self-scanning light-emitting device is provided, this device comprising: a self-scanning transfer element array having such a structure that a plurality of three-terminal transfer elements each having a control electrode for controlling threshold voltage or current are arranged, the control electrodes of the transfer elements neighbored to each other are connected via first electrical means, a power supply line is connected to the control electrodes via second electrical means, and clock lines are connected to one of two terminals other than the control electrode of each of the transfer elements; a light-emitting element array having such a structure that a plurality of three-terminal light-emitting elements each having a control electrode for controlling threshold voltage or current are arranged, the control electrodes of the light-emitting element array are connected to the control electrodes of the transfer element array, and a line for applying a write signal connected to one of two terminals other than the control electrode of each of the light-emitting elements is provided; and a driver circuit for regulating the time duration of on-state of each of the light-emitting elements to correct amounts of light so as to make the distribution of amounts of light uniform.
According to a second aspect of the present invention, a self-scanning light-emitting device is provided, this device comprising: a self-scanning transfer element array having such a structure that a plurality of three-terminal transfer elements each having a control electrode for controlling threshold voltage or current are arranged, the control electrodes of the transfer elements neighbored to each other are connected via first electrical means, a power supply line is connected to the control electrodes via second electrical means, and clock lines are connected to one of two terminals other than the control electrode of each of the transfer elements; a light-emitting element array having such a structure that a plurality of three-terminal light-emitting elements each having a control electrode for controlling threshold voltage or current are arranged, the control electrodes of the light-emitting element array are connected to the control electrodes of the transfer element array, and a line for applying a write signal connected to one of two terminals other than the control electrode of each of the light-emitting elements is provided; and a driver circuit for regulating the voltage of the write signal applied to each of the light-emitting elements to correct amounts of light thereof so as to make the distribution of amounts of light uniform.